Hydraulically Actuated Expanding Spine Cage with Extendable Locking Anchor

ABSTRACT

A spinal implant which is configured to be deployed between adjacent vertebral bodies. The implant has at least one extendable support element with a retracted configuration to facilitate deployment of the implant and an extended configuration so as to expand the implant and effectively distract the disc space, stabilize the motion segments and eliminate pathologic spine motion. Angular deformities can also be corrected, and natural curvatures restored. Preferably, the implant has a minimal dimension in its unexpanded state that is smaller than the dimensions of the neuroforamen through which it typically passes to be deployed within the intervertebral space. The implant is provided with a locking system preferably having a plurality of locking elements to lock the implant in an extended configuration. Bone engaging anchors also may be provided to ensure secure positioning

RELATED APPLICATION DATA

This application is a divisional application of U.S. patent applicationSer. No. 12/548,260, filed Aug. 26, 2009, entitled “HydraulicallyActuated Expanding Spine Cage with Extendable Locking Anchor”, which isa continuation-in-part of U.S. Nonprovisional Patent Application Ser.No. 12/380,840, filed on Mar. 4, 2009, now abandoned, entitled “LockableSpinal Implant,” which is a nonprovisional of U.S. Provisional PatentApplication Ser. No. 61/201,518, filed on Dec. 10, 2008, entitled“Lockable Spinal Implant.” Application Ser. No. 12/548,260 is also acontinuation-in-part of U.S. Nonprovisional Patent Application Ser. No.12/072,044, filed Feb. 22, 2008, entitled “Spinal Implant WithExpandable Fixation.”

This application is also related to U.S. patent application Ser. No.11/692,800, filed Mar. 28, 2007, entitled “Selectively Expanding SpineCage, Hydraulically Controllable in Three Dimensions for Vertebral BodyReplacement,” which is a continuation-in-part of U.S. NonprovisionalPatent Application Ser. No. 11/535,432, filed Sep. 26, 2006, entitled“Selectively Expanding Spine Cage, Hydraulically Controllable in ThreeDimensions for Enhanced Spinal Fusion,” which is a nonprovisional ofU.S. Provisional Patent Application Ser. No. 60/720,784, filed Sep. 26,2005, entitled “Selectively Expanding Spine Cage, HydraulicallyControllable in Three Dimensions for Enhanced Spinal Fusion.”

Each of the above listed applications is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The invention relates to devices and methods for stabilizing thevertebral motion segment. More specifically, the field of the inventionrelates to an expandable spinal implant with locking elements configuredto lock the implant in an expanded configuration within anintervertebral space to provide controlled spinal correction in threedimensions for improved spinal intervertebral body distraction andfusion.

BACKGROUND

A conventional spine cage or implant is characterized by a kidney beanshaped body which is typically inserted posteriorly through theneuroforamen of the distracted spine after a trial implant creates apathway. Existing devices for interbody stabilization have important andsignificant limitations, including inability to expand and distract theendplates or to fix the device in place to prevent relative movementbetween the device and an adjacent vertebral body. Current devices forinterbody stabilization include static spacers composed of titanium,PEEK, and high performance thermoplastic polymer produced by VICTREX,(Victrex USA Inc, 3A Caledon Court; Greenville, S.C. 29615), carbonfiber, or resorbable polymers. Moreover, current interbody spacers donot maintain interbody lordosis and can contribute to the formation of astraight or even kyphotic segment and the clinical problem of “flatbacksyndrome.” Separation of vertebral endplates increases space availablefor the neural elements, specifically the neural foramen. Existingstatic cages do not reliably improve space for the neural elements.Therefore, what is needed is a spinal implant that will provide spacefor the neural elements posteriorly between the vertebral bodies, or atleast maintain the natural bone contours to avoid neuropraxia (nervestretch) or encroachment.

Conventional devices for intervertebral body stabilization includes poorinterface between bone and the biomaterial of the device. Conventionalstatic interbody spacers form a weak interface between bone andbiomaterial. Although the surface of such implants is typically providedwith a series of ridges or coated with hydroxyapetite, the ridges may bein parallel with applied horizontal vectors or side-to-side motion. Thatis, the ridges or coatings on the implant offer little resistance tomovement applied to either side of the endplates. Thus, nonunion iscommon in allograft, titanium and polymer spacers, due to motion betweenthe implant and host bone.

SUMMARY OF THE DISCLOSURE

In one implementation, the present disclosure is directed to a spinalimplant with hydraulically actuatable, locking bone engaging surfaces.The spinal implant includes a housing defining at least two laterallyspaced circular openings; a hydraulic piston disposed in each theopening, each the piston having an outer end movable from a contractedposition within the housing to an extended position out of the housing;a bone engaging surface disposed at each piston outer end; and a lockingmechanism cooperating with the pistons to lock the pistons in theextended position.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, the drawings show aspectsof one or more embodiments of the invention. However, it should beunderstood that the present invention is not limited to the precisearrangements and instrumentalities shown in the drawings, wherein:

FIG. 1 is a perspective view of an intervertebral implant in acontracted configuration embodying features of the invention.

FIG. 2 a perspective view of the implant shown in FIG. 1 in an expandedconfiguration.

FIG. 3 is an exploded perspective view of the implant shown in FIG. 1.

FIG. 4A is a top view of the implant shown in FIG. 1.

FIG. 4B is a side cross-sectional view through line 4B-4B of the implantshown in FIG. 4A.

FIG. 5A is a perspective view of a lower part of the implant shown inFIG. 1 with upper portions and bottom face removed.

FIG. 5B is a bottom view of the lower portion shown in FIG. 5A.

FIG. 6A is a perspective view of the upper portion of the implant shownin FIG. 1 with the lower portion removed.

FIG. 6B is an enlarged perspective view of the staircase-like lower locksupport shown in FIG. 3.

FIG. 7 is a partial side view of one of the locking mechanisms of theimplant shown in FIG. 2.

FIGS. 8A, 8B, 9A and 9B are partial side views of the locking mechanismin FIG. 7 shown in different expanded and locked configurations.

FIGS. 10A and 10B of the locking mechanism illustrate the expanded butunlocked configuration in FIG. 10A and the expanded and lockedconfiguration in FIG. 10B.

FIGS. 11A and 11B are perspective views of the lower lock support andspring locking actuator illustrating the operation thereof.

FIG. 11C is a perspective view of an alternate locking mechanism andlocking actuator embodying features of the invention.

FIGS. 12A, 12B and 12C are perspective views of alternate lower locksupport designs embodying features of the invention.

FIGS. 13A and 13B are perspective and side views respectively of analternative implant embodying features of the invention which has anarticulating top end plate.

FIG. 14A is an exploded perspective view of yet another alternativeimplant embodying features of the invention which has the lower locksupports within the extendable pistons.

FIG. 14B is a top view of the implant shown in FIG. 14A.

FIG. 14C is a side cross-sectional view through line 13C-13C of theimplant shown in FIG. 14B.

FIG. 15 is a perspective view of an alternate implant design havingfeatures of the invention wherein the locking mechanism surrounds acentral opening in the top end plate.

FIG. 16 is a perspective view of an alternate implant design havingfeatures of the invention wherein the expanding piston is centrallylocated and locking mechanisms are provided on both sides of theexpanding piston.

FIG. 17 is a simplified schematic illustration of an alternate implantdesign having ratchet and pawl locking members between the top andbottom plates of the implant.

FIG. 18 is a perspective view of an alternative implant design withratchet and pawl locking members between the top and bottom plates ofthe implant.

FIG. 19 is a cross sectional perspective view of an implant design withratchet and cantilevered spring members between the top and bottomplates of the implant.

FIGS. 20A, 20B, 21A, 21B, 22-26, 27A, 27B, 28 and 29 schematicallyillustrate various means for locking an expanding member of implants inextended configurations embodying features of the invention.

FIG. 30 is a perspective view of yet another alternate implant designhaving features of the invention wherein the locking mechanism hasstraight upper and lower interfitting lock supports.

FIGS. 31A-31G illustrate an alternative implant locking mechanism inwhich a wire-form surrounds a pair of upper support members with groovesconfigured to receive the wire-form.

FIGS. 32A and 32B are perspective views of a further alternativeembodiment of the present invention including locking, conical boneengaging anchors.

FIGS. 33A, 33B and 33C are perspective views showing alternative boneengaging anchors.

FIGS. 34A and 34B are perspective cross sectional views of anotheralternative embodiment of the present invention including locking,screw-threaded bone engaging anchors.

FIGS. 35A and 35B are perspective views of yet another embodiment of thepresent invention including locking, telescoping bone engaging surfaces.

DETAILED DESCRIPTION

FIGS. 1-10B Illustrate an example of an intervertebral implant 10, aSelectively Expandable Cage (SEC), having features of the invention. Theimplant 10 generally includes a housing 11, a housing base 12, aninterlocking top endplate 13, a bottom endplate 14, an interior cavity15 within the housing 11 and a pair of cylinders 16. Upper lock supports17 are attached to the underside of the top endplate 13 and havemulti-stepped lower support surfaces 18 much like an inverted staircase.Lower lock supports 20, having multi-stepped upper support surfaces 21surround cylinders 16 much like an upright staircase. Pistons 22 aresecured to the under surface of top endplate 13. Seal members 23 areslidably disposed within the cylinders 16 and are mounted on pistons 22.The upper surface 24 of bottom end plate 14 is provided with lockingactuator channels 25 which partially receive spring locking actuators26. The base 12 of the housing 11 has arcuate slots 27 which areconfigured to slidably receive the depending elements 28 or lockingactuator transfer element of the lower lock supports 20 and partiallyreceive the spring locking actuators 26. Depending elements 28 engagethe forward end 30 of spring locking actuators 26. The spring lockingactuators 26 are initially in a compressed configuration so that uponthe extension of the top endplate 13 and the attached upper locksupports 17, the lower lock supports 20 rotate about the cylinders 16due to the force applied by the biased spring locking actuator 26. Thiscauses the lock support surfaces 21 of the lower lock supports 20 toengage support surfaces 18 of the upper lock supports so as to lock thetop end plate 13 in an extended configuration. The support surfaces 18of the upper lock supports 17 and the support surfaces 21 of the lowerlock supports 20 are tiered with multiple steps so that the implant 10can be locked at several different expanded heights. The undersidestepped support surfaces 18 of the upper lock support 17 may be providedwith increasing riser height (alignment faces 46) in the upwarddirection to provide smaller incremental expansion near the end of thepiston expansion. In addition or alternatively, the stepped supportsurfaces 21 of the lower lock support 20 may be provided with decreasingriser height in the upward direction for the same reason. A variety ofriser heights of the upper lock support 17 or lower lock support 20 canbe provided. The lowermost stepped support surface 18 of the upper locksupport 17 and the uppermost stepped support surface 21 of the lowerlock support 20 may be provided with various lengths and widths toensure better support.

As can be seen in FIG. 2 there are two sets of upper lock supports 17attached to the top endplate 13 and there are two sets of lower locksupports 20 in this embodiment, but a single set or more than two setsof upper and lower lock supports can also be used to lock the implant 10in the expanded state.

The implant 10 is configured to be implanted between opposing vertebralbodies in the spine to facilitate bony fusion between those vertebralbodies. The implant 10 is shown in its collapsed or contractedconfiguration in FIG. 1 and in one example of its expanded configurationin FIG. 2. In the collapsed state, the implant 10 can be inserted easilyinto the intervertebral body space through a minimal incision and withminimal tissue removal. Once in that space, the implant 10 can beexpanded against the two opposing vertebral bodies to distract them andthereby restore height to the intervertebral space. This provides stableopposition of the implant 10 to both vertebral bodies and optimizes thebony fusion process. The fusion process can also be enhanced by fillingthe interior cavity 15 with autologous bone graft, a bone growthenabling matrix, and/or bone growth stimulating substances prior toand/or after insertion into the body.

Further details of individual parts of the implant 10 are depicted inFIGS. 3, 4A and 4B. Pistons 22 are attached to the underside of the topendplate 13 which are configured to support seal members 23 which runinside of cylinders 16 located in the housing 11. When the cylinders 16are pressurized as will be described in more detail below, the seals 23running inside the cylinders 16 and pistons 22 slidably disposed withinthe seals are vertically displaced, translating the top endplate 13vertically above the housing 11. Lower lock supports 20 are locatedaround the outer wall of the cylinders 16. When the top endplate 13 isvertically displaced, which in turn displaces the attached upper locksupports 17, the lower lock supports are rotated by the biased lockingactuators 26 to a locking position. Arcuate locking actuator channels 25in the top surface of bottom plate 14 and the arcuate slots 27 in thehousing base 12 confines the locking actuators 26 to the housing 11.

Additional details of the housing 11 are depicted in FIGS. 5A and 5B.The housing 11 comprises an outer wall 31 and cylinders 16 which aresecured to housing base 12. The outer wall 31 supports a leading nose 32on the distal end and a delivery boss 33 on the proximal end. Theleading nose 32 has inwardly directed side tapered faces 34 and toptapered face 35 and bottom tapered face 36. These tapered faces 34, 35and 36 enable non-traumatic insertion of the implant 10 passed neuralelements and between the vertebral bodies. The delivery boss 33 containsa delivery tool anchor 37 which allows secure attachment of the implant10 to a delivery tool (not shown), which is illustrated in copendingapplications Ser. No. 11/535,432, filed Sep. 26, 2006, and Ser. No.11/692,800, filed Mar. 28, 2007 for insertion into a vertebral space.The delivery boss 33 also contains pressure input ports 38 which areused to deliver a pressurized fluid to the interiors of cylinders 16.The outer wall 31 of the housing 11 also provides side openings 40 whichprovide space for bony in-growth into central cavity 15 in the housing11 and provide radiolucent openings for the radiographic imaging of theprocess of bony in-growth. The housing base 12 also contains pressurechannels 41 which deliver pressurized fluid from the pressure inputports 38 to the interior of cylinders 16. Although the housing base 12of implant 10 is depicted with independent pressure channel 41 for eachcylinder 16, other embodiments can contain one or more branchingpressure channels for delivering pressurized fluid to two or morecylinders 16. As previously mentioned, the housing base 12 also haslocking actuator slots 27 which hold and guide the locking actuators 26.The locking actuator slots 27 contain a wider portion, locking actuatoropening 42, to enable insertion of the locking actuator 26 into thechannels defined by the locking actuator slots 27 in housing base 12 andthe locking actuator channels 25 in the bottom end plate 14. The housingbase 12 also has optional alignment bosses 19 which align the bottomendplate 14 to the housing 11 via optional alignment holes 9.

FIGS. 6A and 6B illustrate further details of the top endplate 13 andthe lower lock support 20. The two sets of pistons 22 and upper locksupports 17 are joined by connecting members or struts 44. The pistons22 have seal bosses 45 on which the seals 23 are mounted. The upper locksupports 17 have tiered lower support surfaces 18 and risers oralignment faces 46. The tiered or stepped support surfaces 18 of theupper lock supports 17 engage the stepped or tiered support surfaces 21of the lower lock supports 20. The alignment faces 46 of the upper locksupport are configured to engage the alignment faces 47 of the lowerlock supports 20. The uppermost support surface of the lower locksupport 20 has a lock support stop 50 which engages with the lower mostalignment faces 46 of the upper lock support to prevent the lower locksupport 20 from over rotating as it engages the upper lock support 17.The bottom of the lower lock support 20 also has the locking actuatortransfer element 28 which engages the forward end 30 of the springlocking actuator 26 to transfer the actuation force from the lockingactuator 26 to the lower lock support 20.

FIGS. 7 through 10B show details of the selectively expanding lockingsequence of implant 10 with the housing 11 removed. The collapsedconfiguration is shown in FIG. 7 with the support surfaces 18 of theupper lock support 17 resting on the support surfaces 21 of the lowerlock support 20. The locking actuator 26 is a biasing element, such as aspring, that engages the depending element or locking actuator transferelement 28 to urge the alignment faces of the lock supports in adirection where they contact. Thus, in one exemplary embodiment, thealignment faces 47 of the lower lock support 17 are forced against thealignment faces 46 of the upper lock support 17. The lock support stops50 fit within the lower lock stop relief 52 (shown best in FIG. 6A) onthe top endplate 13. When the cylinders 16 are pressurized, the pistons22 raise the top endplate 13 and attached upper lock supports 17(straight arrow) moving the support surfaces 18 of the upper locksupport 17 off of the support surfaces 21 and moving the lower alignmentfaces 46 passed the upper alignment faces 47. When the alignment faces46 of the upper lock support 17 have cleared the alignment faces 47 ofthe lower lock support 20, the locking actuators 26 (in this embodimenta compressed coiled spring) engaging the locking actuator transferelement 28 force the lower lock supports 20 to rotate (curved arrow inFIGS. 8B and 9B). The support surfaces 21 of the rotating lower locksupports 20 move to the next lower level of the support surfaces 18 ofthe raised upper lock supports 17 until the alignment faces 47 of thelower lock supports 20 engage the next level of the alignment faces 46of the upper lock supports 17. The lower lock support 20 and upper locksupport 17 then lock the top endplate 13 at this expanded level. Thisprocess repeats itself at each locking level (FIGS. 8A, 8B, 9A, 9B and10A) until the top level (or somewhere between) is reached as shown inFIG. 10B. At this top level, the locking actuators 26 engage the lockingactuator transfer elements 28 and the lower lock supports 20 are rotatedso the lowermost alignment surface 46 of the upper lock support 17engages lock support stop 50 of the uppermost support surface 21 of thelower lock support 20. At this highest locked level only the lowestsupport surfaces 18 of the upper lock supports 17 and the highestsupport surfaces 21 are engaged providing all of the locking support. Ascan be seen from FIGS. 10A and 10B the lowest support surfaces 18 of theupper lock supports 17 and the highest support surfaces 21 of the lowerlock supports 20 can be wider than the other support faces to providesufficient support material when only these two faces are engaged.

FIGS. 11A and 11B illustrate the operation of locking actuator 26. Inthis embodiment the spring locking actuator 26 is compressed into an arcbeneath the lower lock support 20. One end of the spring lockingactuator 26 is constrained by the housing 11 (not shown) and the otheris engaged with the locking actuator transfer element 28. When the loweralignment faces 46 of the upper lock support 17 are raised above theupper alignment faces 47 of the lower lock support 20 by the extensionof piston 22, the locking actuator 26 pushes against the lockingactuator transfer element 28 and rotates the lower lock support 20 in aclockwise direction (arrow) as viewed from above. It should be notedthat in the embodiment of the current implant as describe thus far, theangular orientation of the tiered upper and lower support surfaces 18and 21 can vary when there is more than one set of supports. As shown inFIG. 3 the proximal lower support surfaces 21 are oriented clockwise asviewed from above and the distal lower support surfaces 21 are orientedcounter-clockwise. This opposite orientation provides enhanced lockingsupport for rotational forces applied to the implant.

An alternate locking actuator 26 a is shown in FIG. 11C as a torsionspring. This locking actuator 26 a has constraining tab 53 secured tothe lower lock support 20 and constraining tab 54 secured to the housing11 a. Just as the compression spring shown in FIGS. 11A and 11B appliesa force to the lower lock support 20 a to rotate it, the torsion springin FIG. 11C does the same. An extension spring would work equally aswell as a locking actuator 26 a. Spring actuators can be made of anappropriate biocompatible material such as stainless steel, NITINOL,titanium or a suitable polymer. Locking actuators are not limited tosprings. A wide variety of mechanisms can be used to actuate the lowerlock supports 20, including but not limited to, a linear drive, anexternally actuated tensile member, a worm gear, an inflated member suchas a balloon or bellows, a magnet, a rotational drive such as a micromotor, a super elastic shape memory element, and the like.

FIGS. 12A through 12C show variations of the lower lock support 20described above. In FIG. 12A a tri-set lock support 20 a is shownwhereby there is are three sets of upper support surfaces 21 a, upperalignment surfaces 47 a and lock support stops 50 rather than the 2 setsdescribed above. This tri-set lower lock support 20 a has two advantagesover the 2 sets design, 1) there are three support columns rather thantwo locking the implant 10 in an expanded state thereby creating a morestable lock and 2) the tri-set lower lock support—20 a has to move orrotate much less for each locking level. This last advantage issignificant when the locking actuator is a spring such as spring lockingactuator 26 as this places less strain on the spring to achieve therequired locking force at each step. Each lower lock support column willhave a corresponding upper lock support column (not shown). The uppersupport surfaces 21 and lower support surfaces 18 are not limited to 2or 3 sets of surfaces. Any number of sets of support surfaces includinga single set may be employed.

FIG. 12B shows an inter-digitating lower lock support 20 b. Each of theinter-digitating upper support surfaces 21 b on the inter-digitatinglock support 20 b is paired with an inter-digitating stop 50 b whichwhen paired with matching inter-digitating support surfaces and stops ofan upper lock support (not shown) prevents the inter-digitating supportsurfaces 21 b from moving relative to the inter-digitating supportsurfaces of an upper lock support to unlock the implant 10 b without theinter-digitating lower support faces first lifting above theinter-digitating stop 50 b. This design provides an enhanced lockingfeature.

Generally the lower support surfaces 18 and the upper support surfaces21 are horizontal to maximize vertical support in the locked implant.However, the locking support 20 c shown in FIG. 12C provides an enhancedlocking feature by providing inclined support surfaces 21 c which have aslope relative to the horizontal which requires matching inclined lowersupport surfaces on the upper lock supports (not shown) to be liftedabove the inclined upper support surfaces 21 c before the upper locksupport can be rotated to unlock the implant 10 c.

FIGS. 12A and 12C show various lengths of locking actuator transferelements or depending elements 28. The locking actuator transfer element28 can vary in length depending on how much engagement is desiredbetween the locking actuator transfer element 28 and the lockingactuator slots 27. The locking actuator transfer element 28 includes oneor more transfer element tabs 29 a and 29 c which vertically constrainthe lower lock support 20 to the locking actuator slots 27 in thehousing 11. The wider locking actuator opening 42 described aboveenables insertion of the locking actuator transfer element 28 withtransfer element tabs 29 a and 29 c into the locking actuator slots 27in housing base 12 at the rotational position where the locking actuatortransfer element 28 is aligned with the locking actuator opening 42. Inother rotational positions the transfer element tabs are constrained bylateral extensions 49 (shown in FIG. 4B) on the sides of the narrowerlocking actuator slots 27. In this manner the locking actuator transferelement 28 provides both the function of transferring force from thelocking actuator 26 to the lower lock support 20 as well as constrainingthe lower lock support 20 to the housing 11. This later functionprevents the frictional forces between the lower alignment faces 46 andthe upper alignment faces 47 created by the biased spring lockingactuator 26 from lifting the lower lock support 20 along with the upperlock support 17 when the upper lock support 17 is lifted by the piston22.

As an alternative to the locking actuator transfer element 28, theembodiment shown in FIG. 12B depicts a locking actuator guide channel80. This locking actuator guide channel 80 engages a tensile member (notshown) which transfers actuation force from the locking actuator 26 tothe lower lock support 20. Tensile members can be an of a number ofknown elements such as sutures made of polymers or natural materials,metal cable, plastic or metal rod and the like.

FIGS. 13A and 13B illustrate an alternate design of an implant 110embodying features of the invention. The implant 110 has independentactuation of the distal piston 122 a and proximal piston 122 b. The twopistons 122 a and 122 b are interconnected by an articulating topendplate 113 which allows independent lift and locking of each side ofthe implant 110. This independent lift and locking of both ends of theimplant 110 enables the implant to conform to intervertebral endplatesthat have uneven lateral heights between them. Further, this independentlift and locking allows the implant 110 to be used to create varyinglateral heights between vertebral endplates which can be useful tocompensate for a scoliosis in the spine.

Implant 110 has a housing 111 which has an alternate delivery toolanchor 160 located in it as well as alternate pressure input ports 137.A variety of anchor design or pressure ports can be used with any of theembodiments of the current device without departing from the scope ofthis invention. Lock and unlock access ports 138 are also located onthis housing 111. These ports are used to guide lock and unlockmechanisms (not shown) which can be manipulated externally to theimplant 110 to actuate the lower lock support 120 to not only move itunder the upper lock support 117 to hold the piston 122 b andarticulating endplate 113 in an expanded position, but also to move thelower lock support 120 away from the upper lock support 117 to allow thepiston 122 b and articulating endplate 113 to collapse back into thehousing 110. This later action maybe desirable to remove the implant 110from or reposition the implant within the intervertebral space. Avariety of lock/unlock mechanism can be used with the current inventionsuch as but not limited by, a tensile member including suture thread andmetallic cable, a compressive member such as a metallic or polymer rod,pressurized fluid, a rotating drive, a super elastic shape memoryelement, and the like.

FIGS. 14A-14C depict yet another alternate implant 210 that embodiesfeatures of the invention. Implant 210 has an interfacing top plate 213which connects to separate and freely rotating pistons 222 via thepiston capture plate 270 on the interfacing top plate 213 and the pistonheads 318 on the rotating pistons 222 ab. The rotating pistons 222 abalso interiorly contain upper lock supports 217 with support faces 218and alignment faces 246. Seals 223 are mounted on the rotating pistons222 ab and the seals 223 and rotating pistons 222 ab fit into internalcylinders 216 that are located on the housing 211. The internalcylinders 216 have lower lock supports 220 with support surfaces 221 andalignment faces 247 as well as lower retaining features 273. The housing211 also contains one or more pressure input ports 238.

In use, the implant 210 is inserted into the intervertebral body spacein a collapsed state and fluid pressure is delivered through thepressure input port(s) 238 to the internal cylinder(s) 216 to raise theseal(s) 223 and rotating piston(s) 222 ab out of the internalcylinder(s) thereby raising the interfacing top plate 213 and expandingthe implant 210. Once the rotating pistons 222 ab have been raised suchthat the lower alignment faces 246 of the upper lock supports 217 havecleared the upper alignment surfaces 247 of lower lock supports 220, anactuator (not shown) rotates the rotating pistons 222 ab such that thelower support surfaces 218 of the upper lock supports 217 are movedabove the upper support surfaces 221 of the lower lock supports 220, tothereby lock the implant 210 in the expanded configuration. The actuatorcan be one or more tensile members such as suture threads or cables thatextend from the user into the implant 210 through the lock and unlockaccess ports 238 on the interfacing top plate 213 to the piston head271. Applying tension to one or more tensile members when the piston isin an extended configuration will rotate the piston heads 271 such thatthe support surfaces 218 of upper lock supports 217 are moved above thesupport surfaces 221 of the lower lock supports 220 thereby locking theimplant 210. Alternately or in addition to applying tension to lock theimplant 210 in an expanded configuration, apply tension to one or moretensile members will rotate the piston heads 271 such that the lowersupport surfaces 218 are moved away from the upper support surfaces 221thereby unlocking the implant 210 and allowing the rotating pistons 22ab 2 to seat back into the internal cylinders 216 such that the implant210 is once again in a collapsed configuration.

FIG. 15 illustrates an alternate implant design 310 embodying featuresof the invention which has a housing 311, top end plate 313 and pistons322 similar to the prior embodiments. This implant 310 has upper locksupports 317 and lower lock supports 320 within a central portion of theimplant. The upper lock supports 317 are secured to the top end plate313 and the lower lock supports 320 are secured to the base 314 withdepending elements (not shown) as was described above and are moved asin the prior embodiments.

FIG. 16 illustrates an alternate implant design 410 embodying featuresof the invention which has a housing 411, top end plate 413 and acentrally located piston 422 similar to the prior embodiments. Thisimplant 410 has upper lock supports 417 and lower lock supports 420distal and proximal to the centrally located cylinder 416 and piston422. The upper lock supports 417 are secured to the top end plate 413and the lower lock supports 420 are secured to the base 412 and aremoved as in the prior embodiments via depending elements (not shown) aswas described above.

FIG. 17 shows another alternate implant 510 which has a pair of pistons522 and which has a locking support system which includes ratchets 520on the base 512 and pawls 517 pivotally mounted to and depending fromthe top end plate 513. Expansion of the pistons 522 causes the free ends518 of pawls 517 to engage recesses 520 in the ratchets 521 so as tolock the top end plate 513 in an extended configuration.

FIG. 18 illustrates another alternative implant design 610 which issimilar to that shown in FIG. 17. In this embodiment the free end of thepawl 617 has a plurality of teeth 618 to provide greater effectivecontact between the pawl 617 and the ratchet 621 for locking of theimplant 610.

FIG. 19 is the cross section of another embodiment of implant 710embodying features of the invention. In this embodiment the pistons 722are surrounded by upper lock support 717 which has at least onecantilever extension ending at the support surface 718. The supportsurfaces 718 are captured by the recessed support surfaces 721 which arelocated on the inner wall of the housing 711. Once the pistons 722 areexpanded in an upward direction, the support surfaces 718 of the upperlock support 717 engages the recessed support faces 721 locking theimplant 710 in place. The upper lock support 717 can be rotated relativeto the piston 722 and housing 711 to disengage the support surfaces 718from the support faces 721 to unlock the implant 710 and lower thepistons 722 as needed. Alternately the implant 710 can be unlocked byrotating the upper lock support constraints 775 relative to the upperlock support 717 to press on the cantilever extensions and disengage thesupport surfaces 718 from the support surfaces 721.

FIGS. 20A-31G illustrate a variety of suitable means for lockingextendable members such as pistons in extended configurations. FIGS.20A, 20B, 21A, 21B, and 22-31G show variations of lower lock supportsand upper lock supports. In each of these variations there are supportsurfaces on the lower lock supports which engage support surfaces on theupper lock supports.

In FIGS. 20A and 20B support surfaces 818 comprise grooves set into theupper lock support 817. The lower lock support 820 is a U-shaped tongwhich is configured to advance (as indicated by the arrow in FIG. 20A)towards the upper lock support 817 and to engage one of the grooves withits upper support surface 821 for locking an implant not shown in thesedrawings. Lower lock support 820 is withdrawn (as indicated by the arrowin FIG. 20B) from the groove to disengage the lower lock support andunlock the implant.

In the variation shown in FIG. 21A, the lower lock support 920 is aplate with an upper lock clearance opening 970 that is shaped to allowpassage of the cylindrical flat sided upper lock support 917 through thelower lock support 920 (arrow). As shown in FIG. 21B, once the lowerlock support 920 is positioned at the desired location it can be rotatedapproximately 90° (arrow) to engage the support faces of the lower locksupport 920 with the support surfaces 918 of the upper lock support 917.The shape of the upper lock support 917 and mating upper lock clearanceopening 970 on the lower lock support 920 are not restricted to theprofile shown in FIGS. 21A and 21B nor is the locking actuationrestricted to 90° rotation of one of the elements but can vary to anynumber of shapes that allow passage in one configuration but constraintwhen one of the elements is moved to another configuration.

In FIG. 22, the upper lock support 1017 is a cylinder with notches cutto create support surfaces 1018. The lower lock support 1020 is apivoting pin 1070 with a pawl 1071 for the lower support surface 1021.In the configuration shown, the support surface is biased as indicatedby the arrow 1072 to allow the upper lock support 1017 to rise with anexpandable member of an implant and to prevent the upper lock supportfrom dropping. This allows the device to lock at each level when thesubsequent support surface 1018 of the upper lock support 1017 engagesthe support surface 1021 of the lower lock support 1020. In thisvariation having features of the present invention, the upper locksupport 1017 can also be lowered by moving the pivoting pin 1070 of thelower lock support 1020 away from the upper lock support 1017 todisengage the support surface 1021 from the support surface 1018.

FIG. 23 shows yet another embodiment having features of the inventionwhere the lower lock support 1120 is a pin configured to engage (arrow)support surfaces 1118 located in the upper lock support 1117. The lowerlock support 1120 does not have to engage the full thickness of theupper lock support 1117 as shown in this figure, nor does the supportsurface 1118 have to extend through the entire thickness of the upperlock support 1117 but rather can engage any portion of the upper locksupport 1117 that is sufficient to lock an implant in position. Thisembodiment also allows a variety of shapes of pins 1120 and matchingsupport surfaces 1118.

In FIG. 24 the lower lock support 1220 is a grip with two pivoting jaws1270, the ends of which have support surfaces 1221. The upper locksupport 1217 has a series of notches 1271 which have the supportsurfaces 1218. A lock actuator such as a compressive spring (not shown)can apply force (as shown by the arrows 1272) to the grip baseextensions 1273 to lock the device. This variation having features ofthe invention allows the upper lock support 1217 to move upwards butprevents downward motion thereof. Downward motion of the upper locksupport 1217 can be allowed by reversing the force on grip baseextensions 1273.

Not all locking systems embodying features of the invention require theengagement of support surfaces of the upper lock supports directly ontop of the support surfaces of the lower lock supports. A frictionalsupport can be created to lock the device as shown in FIGS. 25 through32B.

In FIG. 25 the upper lock support 1317 has one or more flat faces as thesupport surfaces 1318. The lower lock support 1320 has one or morepivoting pawls that have a support surface 1321 that engage the supportsurface 1318 and supports a load (arrow).

In FIG. 26 the upper lock support 1417 has an exterior support face 1418which is gripped by the support face 1421 on the inner diameter of thewrapped lower lock support 1420. This lower lock support 1420 can be atorsion spring that in its free state grips the upper lock support 1417and releases the upper lock support when a force (arrows) is applied toone or more of its ends 1470 as shown to increase the spring's innerdiameter. The reverse is possible where in its free state the lower locksupport 1420 allows movement of the upper lock support 1417 inside theinner diameter. When a tensile force is applied to the ends 1470 toreduce the inner diameter, the lower lock support grips the supportsurface 1418 of the upper lock support 1417 to lock the implant.

FIGS. 27A and 27B show another variation which can be described as acanted washer type device. The lower lock support 1520 is a plate withan upper lock clearance opening 1570 which allows relative movement ofthe upper lock support 1517 as shown in FIG. 27A. When the lower locksupport 1520 is canted as shown in FIG. 28B the edge of the upper lockclearance opening 1570 comprises a lower support surface 1521 whichengages the upper support surface 1518 which is the outer surface of theupper lock support 1517 locking it relative to the lower lock support1520.

Yet another variation of the gripping lock of the current invention isshown in FIG. 28. In this variation the lower lock support 1620comprises of one or more jaws which have support surfaces 1621 that areconfigure to be forced against the support surface 1618 of the upperlock support 1617 to produce friction to lock the device in place.

FIG. 29 illustrates a lower lock support 1720 which comprises a pivotand pawl as has been detailed above. The end of the pawl comprises alower support surface 1721 which engages an upper support surface 1718on the upper lock support 1717. In this embodiment the upper locksupport 1717 is rotated counter clockwise by an expanding element (notshown). This rotation in turn raises the piston 1722 which expands theimplant. In this manner the upper lock support 1817 is integrated intothe lifting mechanism to engage the lower lock support 1720 and lock theimplant as it expands.

FIG. 30 illustrates yet another alternative implant 1810, similar tothat shown in FIG. 1 except that the upper locking member 1817 and lowerlocking member 1818 have a linear shape rather than the arcuate shape ofthe prior embodiments. The implant 1810 generally has a housing 1811, atop plate 1813, a bottom plate 1814, pistons 1822 and cylinders 1816.The upper locking member 1817 has support surfaces 1818 and the lowerlocking member 1820 has support surfaces 1821. The implant 1810 has alocking actuator (not shown).

FIGS. 31A-31G illustrates another implant 1910 embodying features of theinvention which has upper locking members 1917 with grooves 1970 havingsupport surfaces 1918 and lower locking member 1920 with lockingsurfaces 1921. The lower locking member 1920 is a wire-form whichencircles the exterior of both upper locking members 1917 and isconfigured to seat within the grooves 1970. Expansion of the lowerlocking member 1920 (arrows in FIG. 31B) by the locking actuator (notshown) causes the lower locking member 1920 to be pulled out of thegroove 1970 and allows the upper locking member 1917 to rise with theexpansion of the implant. Release of this expansion of the lower lockingmember 1920 (arrows in FIG. 31A) allows the lower locking member 1920 toseat back into the groove 1970 locking the implant 1910.

FIG. 31G illustrates a detail of an alternate implant 1910 a embodyingfeatures of the invention which has upper locking members 1917 a withgrooves 1970 a having support surfaces 1918 a and lower locking member1920 a with locking surfaces 1921 a. The lower locking member 1920 a isa wire-form which encircles the exterior of both upper locking members1917 a and is configured to seat within the grooves 1970 a. The supportsurface 1918 a locks on the supports surface 1921 a when there is acompressive or downward force (hollow arrow) on the upper locking member1917 a locking the implant 1910 a. Upward force or extension (solidarrow) of the upper locking member 1917 a causes the lower lockingmember 1920 a to ride on the disengaging surface 1919 a and out of thegroove 1970 a allowing the upper locking member 1917 a to rise with theexpansion of the implant 1910 a.

In a further aspect of the present invention, a piston/cylinder andlocking arrangement as described above may be used to deploy extendablebone anchors. For example, implant 10A with conical bone engaginganchors 60 as shown in FIGS. 32A and 32B may be constructed with pistons22 and cylinders 16 as described above in connection with implant 10 andshown, for example, in FIGS. 2, 3 and 4B. Implant 10A has a housing 11as previously described and may include other previously describedfeatures such as interior cavity 15 for bone growth stimulatingsubstances. However, in this embodiment, instead of upper interlockingendplate 13, the two pistons 22 individually terminate with conical boneengaging anchors 60. The bone engaging anchors, including sharp leadingtip 62, form surface for engaging the vertebral body.

As shown in FIG. 32A, bone engaging anchors 60 are in a contractedconfiguration, within housing 11, to facilitate insertion of implant10A. Using hydraulic actuation as previously described, bone engaginganchors 60 are moved to an extended configuration as shown in FIG. 32B,wherein at least leading tip 62 extends beyond housing 11 to engage andanchor in the bone. In order to ensure that the bone engaging anchorsremain firmly engaged in the bone, locking mechanisms includingmulti-stepped upper and lower lock supports 17, 20 as previouslydescribed in connection with implant 10 and shown, e.g. in FIGS. 6A-12C,are provided to support each anchor 60 in the extended configuration.With this arrangement, the extended and locked anchor 60 helps to retainthe implant in place.

A variety of alternatives are possible for the bone engaging anchoraccording to the invention as illustrated in FIGS. 33A-C. For example,implant 10B in FIG. 33A includes bone engaging anchors formed as spike60A and blade 60B. Blade 60B can be particularly effective in preventingmotion along the insertion path after deployment. In this case, thelength of the Blade 60B is aligned in the direction shown by arrow A.This is substantially orthogonal to the direction of implantation (arrowB) and would resist movement in that direction. Implant 10F, shown inFIG. 33B includes further possible variations. In this embodiment, thebone engaging anchors are formed as barbed spikes 60C. Barbs 61 alongthe shaft of the spikes resist forces that tend to move the tissue awayfrom the implant along the axis of the anchor (much as the screwthreaded anchor described below would also resist this force). Alsoincluded in implant 10F is a lateral bone engaging anchor 63 foranchoring in laterally oriented tissue. In the illustrated embodiment,lateral anchor 63 includes a plain spike 60A. Lateral anchor 63 isformed in the same manner and with the same components, i.e. piston,cylinder, locking mechanism, etc. as elsewhere described in thisapplication, except that the components are oriented laterally as shown.To provide support for the bone anchor components in this lateralembodiment, housing 11 includes a central member 11A that dividesinterior cavity 15 into two portions. In the configurations of implants10B and 10F, the top of piston 22 can also become a bone engagingsurface when the anchor member is fully received within the bone. FIG.33C shows a further alternative implant 10G, including anchors 65extending obliquely from housing 11, rather than orthogonally. Thisoblique arrangement is helpful in resisting side to side rotationalforces (for example when the patient/spine bends towards the side) andexpansion forces. Once again, obliquely extending anchors 65 areessentially identical to other bone engaging anchors described hereinexcept for the oblique orientation. Here, holes 68 are provided in topendplate 66 for the spikes to pass through. In general, bone engaginganchors according to embodiments of the invention should have arelatively small termination (e.g. tip 62) relative to the size of thepiston diameter so that the force on the piston created by the hydraulicfluid is proportionally a much greater force at the small anchortermination to enhance its ability to extend into hard bony tissues. Itwill also be appreciated by persons skilled in the art that the variousfeatures of the bone engaging elements, e.g. spike, blade, barbs, etc.,described herein may be combined in any desired combination, in additionto the exemplary combinations shown in the figures of the presentapplication.

In another alternative embodiment, illustrated in FIGS. 34A and 34B,implant 10C includes screw-threaded members 64 as bone engaging anchors.Implant 10C also illustrates a further alternative wherein the boneengaging surfaces, such as the anchors, extend from opposite sides ofthe implant. In this exemplary embodiment, interlocking endplate 13 isreplaced with an integrated top endplate 66. Holes 68 are provided forthreaded member 64 to pass through. Persons of ordinary skill in the artwill appreciate that holes 68 will be located as needed; in theillustrated embodiment one is in endplate 66 and the other in bottomendplate 14.

Threaded bone engaging anchors 64 extend outwardly from pistons 22. Inorder to rotate the threaded anchors into the bone when the pistons areextended, the inner wall of housing 11 is provided with a screw-threadedsurface 70 that mates with corresponding threads 71 cooperating withpistons 22. As previously described, seals 23 act between the pistons 22and cylinders 16 to prevent leakage of hydraulic fluid. When fluid ispressurized within the cylinders as described for prior embodiments, thepiston is extended, but also driven in a circular motion by theengagement between threaded surfaces 70 and 71. The screw-threadedanchor 64 is thus driven into adjacent bone as extended.

Once again, locking mechanisms as previously described and shown, forexample, in FIGS. 6A-12C, may be employed to prevent the bone engaginganchors from becoming unengaged from the bone. In the cross sectionalviews of FIGS. 34A and 34B, upper and lower lock supports 17, 20 arevisible around the outside of the piston and cylinders. Alternatively,depending on the depth and pitch of the threaded portions, use of aseparate locking mechanism may not be required. As persons of ordinaryskill will appreciate, the configuration of the threads alone may besufficient to prevent the anchors from backing out.

FIGS. 35A and 35B illustrate a further aspect of the present inventionwherein locking mechanisms as described are utilized to securetelescoping bone engaging surfaces in place. As used herein, telescopingrefers to nested, extendable members including at least one intermediatemember between a base and bone engaging member.

Referring first to FIG. 35A, implant 10D has substantially planar boneengaging members 72. Bone engaging members 72 are thus similar to thebone engaging members of implant 10, but instead individually actuatedwithout interlocking endplate 13. The piston/cylinder arrangement isalso similar to that previously described except that here upper piston74 is received in intermediate piston 80. Intermediate piston is in turnreceived in cylinder 16 as was previously described for piston 22. Upperpiston 74 is sealed against intermediate cylinder 78 of intermediatepiston by upper piston seals 76 (see FIG. 35B).

The telescoping bone engaging members 72 are secured by lockingmechanisms in a similar manner to the earlier described embodiments,with the addition of an upper lock support 82 for the upper piston.Intermediate piston 80 is supported by upper lock support 17 and lowerlock support 20 as previously described. Upper lock support 82 includesupper and lower lock supports 84, 86. Thus, upper piston 74 is securedto upper lock support 84 of the upper lock set. Lower lock support 86 ofthe upper lock set is mounted on top of upper lock support 17 of thelower lock set. One difference from the earlier described embodiments isthat separate spring actuators 26 are not required for the upper lockset as they may be rotated along with the lower lock set by actuators26.

Implant 10E, as shown in FIG. 35B includes a further variation in whichthe planar portion of upper bone engaging surface 88 is effectivelyannular with a conical anchor 90 at the center. Advantages ofembodiments of the present invention including bone engaging anchorsinclude the ability of the anchors to be extended lateral from the longaxis of the implant (i.e., the insertion axis) with a relatively highforce using the relatively small connection to the implant of thehydraulic line. This is an advantage over other methods that requirelarger access or larger connections to the implant for lager tools ornon-hydraulic extension forces to extend the anchors into the hard, bonytissue.

A lateral cage implant, as illustrated for exemplary embodiments of thepresent invention herein, is particularly advantaged by the use ofanchors as described herein because the lateral approach to the spine isa long and narrow approach, which limits the ability of the surgeon touse other instrumentation to extend anchors from the cage (as can bedone more readily, for example, with an anterior approach where theaccess is not as narrow). However, as will be appreciated by persons ofordinary skill in the art, while particular, additional advantages maybe presented in connection with the lateral approach and cages designedtherefore, anchors according to embodiments of the present invention areadvantageous for any approach as they can produce the required extensionforces regardless of patient anatomy or other restrictions on the use ofalternate extension means by the surgeon.

The description herein focused on the manner in which the lockingelements are configured to lock the implant in extended configurations.Although this locking action resists the forces placed on the implantthat would tend to force it back into a collapsed configuration that isnot the only force the locking elements address. Once inserted betweenvertebral bodies the implant is subject to lateral forces and torsionmoments as well as compressive forces. The locking features along withthe other elements of the invention are designed to resist all of theseforces to provide an implant that provides stable fixation anddistraction.

A partial or complete discectomy is usually performed prior to theinsertion of the spinal implant having features of the invention betweenvertebral bodies. The implant is introduced in its unexpanded state toenable it to be inserted posteriorly with minimal trauma to the patientand risk of injury to nerve roots. Once in place the implant can beexpanded to provide both medial and lateral spinal correction. Theimplant has an unexpanded height of about 5 to about 15 mm, typicallyabout 7 mm and is expandable to at least 130% to about 180% of theunexpanded height. Typically the implant is about 9 to about 15 mm wide,typically about 12 mm wide and about 25 to about 55 mm long, typicallyabout 35 mm long to facilitate minimally invasive insertion and therebyminimize trauma to the patient and risk of injury to nerve roots.

Additional details of the implant such as the attachment of hydrauliclines and lines for transmission of a slurry or liquid bone graftmaterial, device and hydraulic fluid delivery accessories and the likecan be found in co-pending applications Ser. No. 11/535,432 filed onSep. 26, 2006 and Ser. No. 11,692,800, filed on Mar. 28, 2007, which areincorporated herein by reference.

It will be appreciated that the implant, including its variouscomponents should be formed of biocompatible, substantiallyincompressible material such as PEEK or titanium, and preferably type6-4 titanium alloy or other suitable materials which will allow for longterm deployment within a patient.

The extension of extendable members or pistons may be individuallycontrolled so that the physician is able to provide a controlled angleof the corrective implant surface. While only two extendable members orpistons are described herein, the implant may be provided with three ormore individually extendable members so that the physician can exercisethree-dimensional control of the implant extension.

While the invention has been described in connection with what arepresently considered to be the most practical and certain preferredembodiments, it is to be understood that the invention is not limited tothe disclosed embodiments and alternatives as set forth above, but onthe contrary is intended to cover various modifications and equivalentarrangements included within the scope of the following claims.

For example, the implants described herein are expanded by hydraulicfluid. Other expansion means may be employed. For example, a screwmechanism may be employed to expand the implant into engagement withadjacent vertebral surfaces. Further, the implant can be provided withload or pressure sensors that register differential pressure andpressure intensity exerted on the engaging surfaces of the SEC by thepatient's vertebrae end plates to generate corrective signals, forexample by computer control, that are used, e.g. by the surgeon or by acomputer controlled mechanism to realign the patient's spine. Theinvention may further include a system that makes these adjustments,responsive to sensor signals, in real time and on a continual basis,such that the shapes of the implant changes to realign the patient'sspine or mechanism. Preferably, such system is contemplated for use insetting the positions of the pistons during installation of the implant.

While particular forms of the invention have been illustrated anddescribed herein, it will be apparent that various modifications andimprovements can be made to the invention. Additional details of thespinal implant devices may be found in the patents and applicationsreferenced herein. To the extent not otherwise disclosed herein,materials and structure may be of conventional design.

Moreover, individual features of embodiments of the invention may beshown in some drawings and not in others, but those skilled in the artwill recognize that individual features of one embodiment of theinvention can be combined with any or all the features of anotherembodiment. Accordingly, it is not intended that the invention belimited to the specific embodiments illustrated. It is thereforeintended that this invention be defined by the scope of the appendedclaims as broadly as the prior art will permit.

Terms such as “element”, “member”, “component”, “device”, “means”,“portion”, “section”, “steps” and words of similar import when usedherein shall not be construed as invoking the provisions of 35 U.S.C§112(6) unless the following claims expressly use the terms “means for”or “step for” followed by a particular function without reference to aspecific structure or a specific action. All patents and all patentapplications referred to above are hereby incorporated by reference intheir entirety.

What is claimed is:
 1. A spinal implant with hydraulically actuatable,locking bone engaging surfaces, comprising: a housing defining at leasttwo laterally spaced circular openings; a hydraulic piston disposed ineach said opening, each said piston having an outer end movable from acontracted position within said housing to an extended position out ofsaid housing; a bone engaging surface disposed at each piston outer end;and a locking mechanism cooperating with said pistons to lock thepistons in the extended position.
 2. The spinal implant of claim 1,wherein said bone engaging surface comprises a bone engaging anchorhaving a sharp leading edge configured to penetrate bony tissue underthe force of the piston.
 3. The spinal implant of claim 2, wherein boneengaging anchors are extendable from more than one side of the implant.4. The spinal implant of claim 2, wherein the bone engaging anchorscomprise at least one of a conical member, a spike, a blade or apyramid.
 5. The spinal implant of claim 4, wherein the bone engaginganchors further comprise at least one barb.
 6. The spinal implant ofclaim 2, wherein said laterally spaced circular openings are formedaround non-parallel central axes.
 7. The spinal implant of claim 6,wherein the circular openings are formed with central axes atsubstantially right angles to each other.
 8. The spinal implant of claim2, wherein: the housing defines a cylinder wall within each circularopening, the cylinder wall spaced from the housing to provide an annularspace there between; and the locking mechanism is slidably disposed insaid annular space.
 9. The spinal implant of claim 8, wherein thelocking mechanism comprises: a first upper arcuate member with steppedengagement surfaces bearing against the piston; a second lower arcuatemember with stepped engagement surfaces opposing and engaging thestepped engagement surfaces of the first upper arcuate member; and abiasing element biasing said first and second arcuate member engagementsurfaces in a contact direction.
 10. The spinal implant of claim 9,wherein the first upper arcuate member is fixed to the piston by alinking member extending over the cylinder wall.
 11. The spinal implantof claim 10, wherein: the bone engaging anchor comprises a screw memberwith bone cutting threads therearound; the first upper arcuate memberhas screw threads disposed on an outer surface thereof; and the circularopening in the housing is defined by an inner wall having at least inpart screw threads disposed thereon and mating with the screw threads onsaid the first upper arcuate member such that outward movement of thepiston in response to hydraulic pressure in the cylinder causes rotationof the bone engaging anchor as it is extended outward.
 12. The spinalimplant of claim 1, wherein said hydraulic piston is a first piston andthe implant further comprises an intermediate piston disposed betweenthe first piston and the housing, the intermediate piston also definingan intermediate cylinder receiving the first piston therein.
 13. Thespinal implant of claim 12, wherein: the housing defines a cylinder wallwithin each circular opening, the cylinder wall spaced from the housingto provide an annular space therebetween; the intermediate pistons arereceived within base cylinders defined by said cylinder walls; and atleast one locking member is slidably disposed in said annular space. 14.The spinal implant of claim 13, wherein the locking mechanism comprises:an upper arcuate member with stepped engagement surfaces secured to thefirst piston and configured and dimensioned to be received in saidannular space; a lower arcuate member with stepped engagement surfacesslideably disposed in said annular space; an intermediate arcuate memberwith upper and lower facing stepped engagement surfaces secured to theintermediate piston and configured and dimensioned to be received insaid annular space with the upper engagement surfaces opposing andengaging the upper arcuate member engagement surfaces and the lowerengagement surfaces opposing and engaging the lower arcuate memberengagement surfaces; and a biasing element acting on the lower arcuatemember to cause engagement of said stepped engagement surfaces.
 15. Thespinal implant of claim 14, wherein said bone engaging surface comprisesa bone engaging anchor having a sharp leading edge configured topenetrate bony tissue under the force of the piston.